Electrical wiring boxes are often made from nonmetallic materials, typically thermoplastic or thermosetting resins with flame retarding agents. Plastic electrical wiring boxes have various advantages but present difficulties in completely grounding the wiring devices and simultaneously providing a quick and secure way of mounting wiring devices thereon.
Both the mounting yoke and the mounting screw of wiring devices mounted in such boxes should be electrically connected to ground. The mounting strap or the mounting screw may become energized by contacting a current bearing conductor of an electrical cable. If the wiring device is not properly grounded, the metal face plate in contact with the mounting strap or screw becomes a potential source of an electric shock. This problem is especially acute in nonmetallic boxes since they are not normally provided with a grounding lug.
Numerous grounding devices or assemblies are described in the prior art to provide electrical contact between the mounting screw of a wiring device and the electrical cable ground wire including clips, springs, or other devices which firmly engage the mounting screw. Examples of these prior art devices are disclosed in the following U.S. Pat. Nos. 2,149,719 to Arnest; 3,119,895 to Palmer; 3,210,458 to Palmer; 3,575,313 to Trachtenberg et al; 4,315,100 to Haslbeck et al; and 4,392,012 to Nattel.
However, these prior art grounding devices suffer from many disadvantages. For example, these devices are usually formed of a thick rigid metal, and thus, generally do not permit a quick set mounting screw to pass therethrough into the wiring box and still maintain firm electrical contact between the mounting screw and the grounding plate. Moreover, many of the prior art grounding devices require bending the clip into intricate shapes or bending the clip to secure it to the wiring box, and thus, are either expensive to make or difficult to assemble.